flexible intake system for a two-stroke internal combustion engine with additional air supply, comprising a baffle to secure ducts to the cylinder wall

ABSTRACT

This invention relates to a flexible intake system for a crankcase scavenged two-stroke internal combustion engine ( 10 ) having an additional air supply to its transfer ducts. The intake system comprises a flexible intake duct ( 22 ) connecting a fuel supply unit ( 21 ) e.g. a carburettor with an engine cylinder ( 11 ) and at least one flexible air duct ( 40 ) connecting a valve housing ( 42 ) for additional air with the engine cylinder. The end portion of the flexible intake duct ( 22 ) and at least one air duct ( 40 ) is secured to the cylinder by means of a baffle ( 23 ) made of a stiffer material than the ducts ( 22, 40 ) themselves.

TECHNICAL FIELD

This invention relates to a flexible intake system for a crankcasescavenged two-stroke internal combustion engine having an additional airsupply to its transfer ducts, the intake system comprising a flexibleintake duct connecting a fuel supply unit e.g. a carburettor with anengine cylinder and further comprising at least one flexible air ductconnecting a valve housing for additional air with the engine cylinder.

BACKGROUND OF THE INVENTION

Internal combustion engines of the type mentioned above are intended tobe used for driving different kind of hand held tools such as chain sawsand power cutters. In order to decrease the vibrations transferred fromthe engine to the handle portion the engine is usually separated fromthe handle portion by means of a flexible damping arrangement and tofurther decrease the vibrations usually certain details of the masssystem, such as the carburettor, the air filter system and the fuel tankare usually secured to the handle portion. This also decreasesvibrations for the carburettor thereby increasing carburettorreliability. Consequently there is a demand for flexible connectionsbetween the different details on the handle portion and the engine butsince these connections have to be secured to the engine at a ratherconcentrated area the assembling procedure becomes complicated. Inparticular the assembling procedure for securing the different intakeducts for mixture and air to the cylinder of the engine is timeconsuming and it is also difficult to dismount the arrangement whenmaking maintenance and repairing the hand held tool. Further there is aneed for a more stable and reliable fastening arrangement for thedifferent ducts.

SUMMARY OF THE INVENTION

The purpose of this invention is to eliminate or at least reduce thedrawbacks mentioned above in order to get a simple arrangementconnecting the cylinder of the engine with the different ducts therebyfacilitating assembly and dismounting. This is achieved by means of adevice having the characteristics mentioned in the claims.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be described in the following with reference to theaccompanying drawing figures, which show two preferred embodiments ofthe invention.

FIG. 1 is a vertical section of a first embodiment of a hand held toolprovided with the invention.

FIG. 2 is an enlarged view of a part of FIG. 1.

FIG. 3 is a perspective view of a detail of the embodiment in FIG. 1.

FIG. 4 is an exploded view of some details according to the arrangementin FIG. 1-3.

FIG. 5 a is a front perspective view of a second embodiment of theinvention whereas FIG. 5 b is a rear perspective view of said secondembodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The arrangement shown in FIG. 1-3 comprises a two-stroke internalcombustion engine 10 having a cylinder 11 with a cylinder bore 12 inwhich a piston 13 is movable. The piston 13 is via a piston rod 14connected to a crankshaft 15 rotating in a crankcase 16. The cylinder isin a conventional way provided with an exhaust outlet 17, connected to amuffler 18, and with a spark plug 19. Further there is a fuel tank 20 towhich a carburettor 21 is connected.

The carburettor 21 is via an air/fuel duct 22 connected to a baffle 23that is secured to the cylinder 11. The air/fuel duct 22 is made of aflexible material such as rubber or plastic whereas the baffle ismanufactured of a stiffer material such metal or a heat resistingplastic. The baffle 23 comprises a plate shaped lower part 24 providedwith one opening 25 in which one end of the air/fuel duct 22, that isprovided with an end flange 26, is inserted. The end flange 26 rests ina recess 27 arranged around the edge of the opening 25 at the side ofthe baffle 23 that faces the cylinder 11 and serves as a sealing againsta flat seat portion 28 arranged at the cylinder 11 around an inletopening 29 for the air/fuel supply. Preferably the shape of the recess27 is such that it is more narrow close to the edge of the opening thanit is at a distance from the opening thereby safeguarding that the endflange 26 does not fall out of the recess 27. There also is anadditional flange 26 a arranged at a distance from the end flange 26 andsafeguarding that the baffle 23 is clamped at the outer end of theair/fuel duct 22 between the flanges.

The upper portion of the baffle 23 is provided with an L-shaped part 30(as seen in a vertical section) having a first leg 31 (see FIG. 2-3)that is mainly parallel to an outer surface 32 of the cylinder 11, saidsurface being inclined about 45° with respect to the flat seat portion28, and a second leg 33 that is provided with an opening 34 throughwhich a screw 35 is inserted and fixed to the cylinder. The lowerportion of the baffle 23 is provided with an end portion 36 that isclamped between a yoke member 37 (see FIG. 4) fixed to the cylinder bymeans of screws inserted through openings 38 arranged in the yoke memberand secured to the outside of the cylinder wall.

The plate shaped lower part 24 of the baffle 23 is provided with twoadditional openings 39 that in the similar way as the lower opening 25each are connected to an air duct 40 of flexible material. The openings39 are aligned with air transfer ducts inlets (not shown in FIG. 1-4)arranged at the flat seat portion 28 close to the inlet 29 for theair/fuel supply. One end of each air duct 40 is connected to an airinlet 41 via a valve arrangement 42 in order to supply additional air tothe transfer ducts whereas the other end of the air duct 40 is providedwith an end flange 40 a inserted in a corresponding recess 39 a arrangedaround the openings 39 of the baffle 23. Each air duct is also providedwith an additional flange 40 b operating in the similar way as theadditional flange 26 a described above. Also the air inlet side of thecarburettor 21 is connected to said air inlet 41. There is an impulsenozzle 62 pressed into the baffle. An impulse hose 61 is attached to it.

The air inlet 41 constitutes an internal channel within a bracket 43that is secured to handle part 44 of the hand held tool together withthe fuel tank 20. The handle part 44 is separated from the engine 10 andthe tool driven by the engine by means of a flexible support arrangement(not shown) that dampens the vibrations from the engine to the handle.

The upper part of the bracket 43 constitutes a main filter bottom 45supporting a sealing 46 on which a main filter 47 is placed. The mainfilter 47 is clamped between the sealing 46 and a filter cover 48comprising a lower and an upper cover part 49, 50 enclosing a prefilter51 for the flow of air from the atmosphere to the air inlet 41. Thefilter cover 48 is secured to the handle part 44 by means of one orseveral screws 52. The main filter bottom 45 is also provided with anopening 53 placed in line with the axial direction of the screw 35 suchthat the screw can be removed in order to remove the baffle 23. Thisopening is normally covered by the sealing 46. The screw 35 is inclineddownwards, i.e. its lower end is pointing somewhat towards the crankcase16, and preferably more than 20° and less than 40°.

The arrangement mentioned above is assembled in the following manner. Ina pre-mounting stage the air/fuel duct 22 as well as the air ducts 40are inserted into the openings 25 and 39 of the baffle 23 such that theend flanges 26, 40 a are taken up by the recesses 27, 39 a, whereas theflanges 26 a serve as clamping means for the baffle 23. Then thecarburettor 21, the valve arrangement 42 and the bracket 43 with themain filter bottom 45 are secured to the different ducts such that thecomplete arrangement can be treated as one unit. This unit is thenfastened to the cylinder by pushing the end portion 36 of the baffle 23in between the yoke member 37 and the cylinder wall such that the endflanges 26, 40 a create a sealing between the baffle 23 and the seatportion 28. Simultaneously the second leg 33 of the L-shaped part 30will come into engagement with the corresponding surface of the cylindersuch that the screw 35 can be inserted through the opening 53 of themain filter bottom 45 and be fixed to the cylinder 11. Then the sealing46 and the main filter 47 is placed on the main filter bottom 45 andfinally the filter cover 48 with the pre-filter 51 is placed on top ofthe main filter and is secured to the handle portion by means of thescrew 52 and additional screws if necessary.

The second embodiment of the invention according to FIGS. 5 a and 5 bdiffers from the first embodiment in that the air/fuel duct 22′ as wellas the air ducts 40′ are secured to the baffle 23′ by means of moldingor vulcanizing methods or by means of chemical bindings. Also in thisembodiment the ducts are arranged through the openings in the baffle 23′such that the ends create a sealing at the side facing the seat 28′ ofthe cylinder of the engine 10′. FIG. 5 a also shows the inlet ports 54′of the air ducts 40′. A number of sealing ridges 55′, 56′, 57′ areformed in the flexible material facing the seat 28 of the cylinder 11′.Each ridge encloses an inlet port 54′, 61′ provided in the seat 28′.Each ridge is surrounded by a ditch 58′, 59′, 60′. For this embodimentthere is a ditch on both sides of each ridge. This is useful when theridge is pressed against seat 28′.

For the other embodiment as seen in FIG. 2 sealing ridge 56 is enclosedby an outer ditch 59. This figure is schematic as ridge 56 will becompressed and not seat 28.

1. A flexible intake system for a crankcase scavenged two-strokeinternal combustion engine (10) having an additional air supply to itstransfer ducts, the intake system comprising a flexible intake duct (22;22′) connecting a fuel supply unit (21) e.g. a carburettor with anengine cylinder (11; 11′) and further comprising at least one flexibleair duct (40; 40′) connecting a housing (42) for additional air with theengine cylinder, and an end portion of the flexible intake duct (22;22′) and of the at least one air duct (40; 40′) is secured to thecylinder by means of a baffle (23; 23′) made of a stiffer material thanthe ducts (22, 40; 22′, 40′) themselves, characterized in that thebaffle is provided with a first end portion (36) arranged to be insertedbetween a holder means (37) and the cylinder wall.
 2. System accordingto claim 1, wherein the baffle is provided with a second end portion(30) arranged at the opposite side of the baffle (23) with respect tothe first end portion (36) said second end portion being provided with asecuring means (35) such as a screw.
 3. System according to claim 2,wherein the second end portion (30) is provided with a securing means inthe form of at least one screw (35), which screw/s is inclineddownwards, i.e. its lower end is pointing somewhat towards a crankcase(16) of the engine, with respect to an axes perpendicular towards a flatseat (28) for the baffle (23) arranged on the cylinder wall.
 4. Systemaccording to claim 3, wherein the screws (35) are inclined more than 15°downwards but less than 60° downwards, and preferably more than 20° andless than 40°, compared to an axis perpendicular towards the flat seat(28).
 5. System according to any of the previous claims, wherein thebaffle (23) is provided with a flat portion (24) that rests against aseat (28) arranged at the cylinder wall and being provided with inletopenings for the air/fuel and for the additional air.
 6. Systemaccording to claim 1, wherein at least one of said ducts (22, 40; 22′,40′) comprise an end flange (26, 40 a) that is inserted through anopening (25, 39) in the baffle (23; 23′) and that serves as a sealingagainst the cylinder wall.
 7. System according claim 1, wherein at leastone of the ducts (22, 40; 22′, 40′) is secured to the baffle (23; 23′)by means of vulcanization or by molding or chemical binding methods. 8.System according to claim 7, wherein at least one and preferably all ofthe ducts (22′, 40′) is secured to the baffle by means of a moldingmethod used for the ducts, molding through a number of apertures in thebaffle.
 9. System according to claim 1, wherein a number of sealingridges (55-57; 55′-57′) are formed in the flexible material facing aseat (28; 28′) of the engine cylinder.
 10. System according to claim 1,wherein at least one of said ducts (22, 40; 22′, 40′) is made of rubberor plastic.
 11. System according to claim 1, wherein said baffle(23;23′) is made of a heat resistant plastic or a metal such as steel oraluminum.
 12. System according to claim 6, wherein the edge of saidopening (25, 39) is provided with a recess (27, 39 a) facing thecylinder and in which the end flange (26,40 a) is placed.
 13. Systemaccording to claim 12, wherein said recess (27, 39 a) has such a shapethat it is more narrow close to the edge of the opening than it is at adistance from the opening.